Receiver Function Analysis using Ocean-bottom Seismometer Records around the Kii Peninsula, Southwestern Japan

Recent progress on receiver function (RF) analysis has provided us with new insight about the subsurface structure. The method is now gradually being more applied to records of ocean-bottom seismometers (OBSs). In the present study, we conducted RF analysis using OBS records at 32 observation sites around the Kii Peninsula, southwestern Japan, from 2003 to 2007 (Mochizuki et al., 2010, GRL). We addressed problems concerning water reverberations.

We first checked the effects of water reverberations on the OBS vertical component records by calculating vertical P-wave RFs (Langston and Hammer, 2001, BSSA), where the OBS vertical component records were deconvolved by stacked traces of on-land records as source functions. The resultant RFs showed strong peaks corresponding to the water reverberations. Referring to these RFs, we constructed inverse filters to remove the effects of water reverberations from the vertical component records, which were assumed to be represented by two parameters, a two-way travel time within the water layer, and a reflection coefficient at the seafloor. We then calculated radial RFs using the filtered, reverberation-free, vertical component records of OBS data as source functions. The resultant RFs showed that some phases at later times became clearer than those obtained by an ordinary method.

From the comparison with a previous tomography model (Akuhara et al., 2013, GRL), we identified phases originating from the oceanic Moho, which delineates the relationship between the depth of earthquakes and the oceanic Moho: seaward intraslab seismicity is high within the oceanic crust while the landward seismicity is high within the oceanic mantle. This character may be relevant to the dehydration process.